This research deals with several aspects of the biological role played by tumor seeking humoral immune components in tumor growth and spread. The first aspect deals with tumor-localizing (or tumor synthesized) Fc-receptor-like material (FcR-lm). We carry out a longitudinal study in which circulating levels of FcR-lm are monitored in mice as a function of tumor development. FcR-lm is determined in normal mice, in the same mice after being subjected to chemical carcinogenesis or cell inocula of recently induced tumors and in the same mice after tumors have appeared. In all cases we use carcinogen and tumor-cell sub-threshold doses that produce 40%-60% tumor incidence. This experimental layout permits the assessment of progressive alterations, if occurring, of FcR-lm levels in mice during the carcinogenesis-latency and the tumor-bearing periods. Moreover a comparison is feasible between FcR-lm levels in carcinogen or tumor-cell-treated mice that developed tumors and those in similarly treated mice that did not. We also study the effect of tumor growth of deliberate alterations in in-vivo levels of FcR-lm in normal and in carcinogen or tumor treated mice. The second aspect deals with possible immunoregulatory functions of tumor localizing antibodies directed against T cells. We study the in-vivo effects of such antibodies on various T cell functions of otherwise normal mice and on the development of chemically-induced primary and transplanted tumors. The logistics involved in these experiments are the same as described above. The third aspect deals with the possibility to exploit the fact that some tumor-derived anti tumor antibodies express binding constants to cellular (rather than to soluble) tumor antigens. We use such antibodies after radiolabeling as specific homing devices for the purpose of detection, and tracing occult tumor foci. The last question under investigation is whether metastatic tumor variants evoke different expressions of systemic and local humoral immunity than low-metastasis variants.